Aang’s absence from the world for a hundred years changed a great many things, chief among them the rise of the Fire Nation as a colonizing empire. However, Aang could have also delayed the Avatar cycle by quite a bit, which, according to one theory, might be the reason why Sokka’s first girlfriend turned into the moon.
In Avatar: The Legend of Korra, we see that the next Avatar is a member of the Water Tribe, specifically the daughter of the chief of the Northern Water Tribe, which was Korra. However, there was another person who fit that exact same description, who would have been born right around the time Aang would have died had he not frozen himself for a hundred years.
Princess Yue could have been the Water Avatar after Aang
Yue was the daughter of the Chief of the Nothern Water Tribe, who was born ‘sleeping” i.e. without a soul. The theory states that that Yue, who more or less matches Korra in description was destined to be the next Avatar, but since Aang was frozen in ice, her soul was never freed to be born with her, and so the powers of the Moon Spirit needed to be borrowed to bring the child to life.
The Avatar Spirit is actually the Spirit of Light called Raava, who fused with the first Avatar, Wan, to allow him to bend all the four elements. However, the spirit also gave Wan the ability to reincarnate after death and communicate with his successors. This ability to reincarnate was halted when Aang was in suspended animation, causing the child who was supposed to inherit the spirit, to be born without one.
The Avatar cannot access their predecessors anymore
The Legend of Korra greatly expanded on the Avatar lore, bringing us the origin of the Avatar Cycle. While Aang was able to use the powers of his predecessors and so was Korra, her encounter with her evil uncle, who became the Dark Avatar after uniting with the Spirit of Darkness, Vaatu, caused her to lose her connection to her predecessors.
This would mean, that the Avatar that came after Korra, an Earth Bender, would probably only have Korra to ask for guidance, rather than the thousands of years of history and abilities that were available to the previous Avatars. However, given that Avatars tend to be able to fix what their immediate predecessor could not, it is possible that the Earth Avatar after Korra could restore the Avatar Cycle, or gain access to the past Avatar’s knowledge somehow.
